Meaning

noun an involuntary orienting response; positive or negative reaction to a stimulus source

originFrom -tropism (suffix meaning ‘growth towards; movement, turning’) (possibly based on geotropism and heliotropism), from Latin tropus + English -ism (suffix forming nouns of action, process, or result). Tropus is derived from Ancient Greek τρόπος (trópos, “a turn; a manner, style, way; figure of speech, trope; etc.”), from τρέπω (trépō, “to turn; to divert; to rotate or change orientation”) (from…

Etymology from Wiktionary, CC BY-SA 3.0